Type II diabetes is the most prevalent form of diabetes. The disease is caused by insulin resistance and pancreatic β cell failure, which results in decreased glucose-stimulated insulin secretion. Fibroblast growth factor (FGF) 21, a member of the FGF family, has been identified as a metabolic regulator and is preferentially expressed in the liver and adipose tissue and exerts its biological activities through the cell surface receptor composed of FGFR1c and β-Klotho on target cells such as liver and adipose tissues (WO0136640, and WO0118172). The receptor complex is thought to trigger cytoplasmic signaling and to up-regulate the GLUT1 expression through the Ras/MAP kinase pathway. Its abilities to provide sustained glucose and lipid control, and improve insulin sensitivity and β-cell function, without causing any apparent adverse effects in preclinical settings, have made FGF21 an attractive therapeutic agent for type-2 diabetes and associated metabolic disorders.
There have been a number of efforts towards developing therapies based on FGF21. WO2006065582, WO2006028714, WO2006028595, and WO2005061712 relate to muteins of FGF21, comprising individual amino-acid substitutions. WO2006078463 is directed towards a method of treating cardiovascular disease using FGF21. WO2005072769 relates to methods of treating diabetes using combinations of FGF21 and thiazolidinedione. WO03059270 relates to methods of reducing the mortality of critically ill patients comprising administering FGF21. WO03011213 relates to a method of treating diabetes and obesity comprising administering FGF21.
However, many of these proposed therapies suffer from the problem that FGF21 has an in-vivo half-life of between 1.5 and 2 hrs in humans. Some attempts have been made to overcome this drawback. WO2005091944, WO2006050247 and WO2008121563 disclose FGF21 molecules linked to PEG via lysine or cysteine residues, glycosyl groups and non-natural amino acid residues, respectively. WO2005113606 describes FGF21 molecules recombinantly fused via their C-terminus to albumin and immunoglobulin molecules using polyglycine linkers. However, developing protein conjugates into useful, cost-effective pharmaceuticals presents a number of significant and oftentimes competing challenges: a balance must be struck between in vivo efficacy, in vivo half-life, stability for in vitro storage, and ease and efficiency of manufacture, including conjugation efficiency and specificity. In general, it is an imperative that the conjugation process does not eliminate or significantly reduce the desired biological action of the protein in question. The protein-protein interactions required for function may require multiple regions of the protein to act in concert, and perturbing any of these with the nearby presence of a conjugate may interfere with the active site(s), or cause sufficient alterations to the tertiary structure so as to reduce active-site function. Unless the conjugation is through the N′ or C′ terminus, internal mutations to facilitate the linkage may be required. These mutations can have unpredictable effects on protein structure and function. There therefore continues to be a need for alternative FGF21-based therapeutics.
The reference to any art in this specification is not, and should not be taken as, an acknowledgement of any form or suggestion that the referenced art forms part of the common general knowledge.